Compositions for gaskets having improved resistance to water-based aerosol products

ABSTRACT

COMPOSITIONS FOR USE AS SEALING GASKETS IN AEROSOL MOUNTING CUPS, WHICH CONTAIN A PEPTIZED POLYCHLOROPRENE RUBBER DISSOLVED IN A VOLATILE ORGANIC SOLVENT AND A TERNARY CURING SYSTEM CONSISTING OF DI-O-TOLYGUANIDINE, 2-MERCAPTOIMIDAZOLINE AND DIPENTAMETHYLENETHIURAM HEXASULFIDE. ADDITIONAL INGREDIENTS SUCH AS FIBERS, PLASTICIZERS, ANTIOXIDANTS AND PIGMENTS MAY BE INCOPORATED TO MODIFY   CERTIN PROPERTIES OF THE COMPOSITIONS AND OF THE GASKETS MADE FROM THEM.

Jilly 18, 1972 p. EDMQNSTQ'N ET AL 3,677,993

COMPOSITIONS FOR GASKETS HAVING IMPROVED RESISTANCE TO WATER-BASEDAEROSOL PRODUCTS Filed March 10, 1970 INVENTORS ROBERT P. EDMONSTON JOELA. GRIBENS CHARLES W. SIMONS United States Patent US. Cl. 26033.6 AClaim ABSTRACT OF THE DISCLOSURE Compositions for use as sealing gasketsin aerosol mounting cups, which contain a peptized polychloroprenerubber dissolved in a volatile organic solvent and a ternary curingsystem consisting of ,di-o-tolylguanidine, 2-mercaptoimidazoline anddipentamethyleuethiuram hexasulfide. Additional ingredients such asfillers, plasticizers, antioxidants and pigments may be incorporated tomodify certain properties of the compositions and of the gaskets madefrom them.

THE PRIOR ART Pressurized aerosol containers are increasingly used inpackaging and dispensing a wide variety of materials. In this type ofapplication, the product to be dispensed is confined under pressure bymeans of a volatile propellant and is discharged in a controlled mannerthrough a valveactuated orifice. A typical aerosol unit is composed of ahollow cylindrical container closed at one end and provided with anopening at its opposite end for receiving a dispensing valve assembly. Ametal mounting cup serves as a closure for the container and also as asupport for the valve assembly which is tightly fitted within anaperture centrally located in the cup. The mounting cup carries anannular gasket which is adapted at its outer edge to be rolled andcrimped to the walls forming the opening in the container and therebyform a seal upon crimping.

The gasketing material used in aerosol mounting cups should be elasticand resilient so that it yields under deforming forces to establish asatisfactory seal when the cup is crimped to the container and tomaintain the seal over normal storage periods. Among the gasketsemployed are those of the flowed-in type prepared from solventbasedrubber compositions comprising an elastomer dissolved in a volatileorganic solvent. These compositions may also contain pigments, fillers,curing agents and other compounding ingredients. Because neoprene (achlorobutadiene polymer) possesses superior resistance to oxidation,oils, propellants and many chemicals found in aerosol containers, it ismost widely used in such compositions. Neoprene is dissolved in asuitable solvent, such as toluene, to assist in uniformly depositing thecomposition in the mounting cup. In preparing gaskets from thesecompositions, a band of the fluid material is deposited in the channelof the mounting cup 'while the cup is being rotated beneath a meteringnozzle through which the composition flows to form a continuous deposit.Thereafter the deposit in the cup is converted into a dry solidelastomeric sealing mass by expelling the solvent and curing it atelevated temperatures.

While gaskets derived from compositions containing neoprene performadmirably in many aerosol containers, the gaskets are vulnerable toattack when used to seal water-in-oil emulsion packed products, such asinsecticidal compositions, window cleaning compositions, simulated snowcompositions for decorative purposes and other spray type packages. Insuch packages the emulsion attacks the neoprene gasket and causes it todegrade. Degra- 3,677,993 Patented July 18, 1972 ice dation results inflaking of the gasket which in turn adversely affects the performance ofthe aerosol unit. For example, the valve may become clogged due to thedeposition and accumulation of the flaked solid rubber particles aroundthe valve orifice and in the passageways leading to the orifice. Valveleakage is also a frequent source of trouble due to the flaked particlespresent in the valve seat which prevent the valve from closing properlyand allow the propellant to escape. Another common problem is that theflaked particles settle and either aggravate the valve clogging or theymay entirely prevent discharge of the product.

In general, a high degree of resistance to such waterbased products canbe obtained by increasing the number of crosslin'kages between polymermolecules. Crosslinking is effected by curing agents in the presence ofcure accelerators. However, the presence of accelerators in the liquidcomposition can greatly decrease its storage stability due to anincrease in viscosity. Storage stability is a necessary property whichthe composition must possess if it is to be properly lined in mountingcups.

SUMMARY OF THE INVENTION According to the present invention, it is nowpossible to line mounting cups with curable neoprene-basedgasket-forming compositions and obtain gaskets which overcome thedrawbacks of conventional gaskets in the presence of water-in-oilemulsion packs. This is accomplished by the use of a ternary curingsystem consisting of di-otolylguanidine, Z-merca-ptoimidazoline anddi-pentamethylenethiuram hexasulfide. Chloroprene rubber compositionscontaining this ternary curing system not only yield gaskets withoutstanding resistance to degradation by water-based aerosol products,but they also possess the necessary storage stability which renders themindustrially useful.

DESCRIPTION OF THE DRAWING The present invention will be more clearlyunderstood on reference to the accompanying drawing and to thediscussion relating thereto:

FIG. 1 is a side elevational view of a typical aerosol containerprovided with a mounting cup and valve unit.

FIG. 2 is an axial sectional view of the aerosol mounting cup of FIG. 1carrying a gasket prepared from compositions of the present invention.

'FIG. 3 is a fragmentary axial sectional view of the upper portion ofthe aerosol container of FIG. 1 showing the gasketed mounting cup ofFIG. 2 crimped in position over the mouth of the container.

Referring to FIG. 1, a typical aerosol container is illustrated whichcomprises a cylindrical body portion 10 fitted with a domed top portion12 and a bottom closure 11. The container is provided with a meteringvalve generally designated at 13 which is actuated by button 15. Theactuator button is carried on a hollow valve stem 14 and is providedwith an orifice 16 through which the container contents are dischargedwhen valve 13 is opened. Communicating with valve 13 is a dip tube 17which is of sutficient length to allow the contents to be dischargedfrom the container. The valve unit, which may be any of the varioustypes known to the art, is supported by a mounting cup, generallydesignated at 18, which is adapted to receive the valve stem 14. Themounting cup also serves as a closure for the container and carries thesealing gasket in the annular channel 22 which is applied over theopening in the domed top portion 12 of the container.

An axial sectional view of mounting cup 18 is shown in FIG. 2 ininverted position relative to its placement in the assembled container.The cup comprises a circular panel 19 having an integral skirt 20depending from its periphery. The free edge of skirt 20 is outwardlyflanged at 21 to form an annular gasket-receiving channel 22. The innerportion of panel 19 is countersunk to form a tubular recess, generallydesignated at 23, which has a dependent circular wall 24 integrallyjoined with an apertured horizontal wall 25. When the cup is placed insealing position, the tubular recess 23 acts as a pedestal for the valveunit and the valve stem is admitted into the container through aperturedwall 25. The gasket 26 is disposed predominantly in the annular channel22 of the cup.

FIG. 3 shows the gasketed mounting cup of FIG. 2 crimped on positionover the mouth of an aerosol container. As illustrated in FIG. 3, theopen end of domed portion 12 of the container is provided with anoutwardly curled peripheral head 27 which defines the container mouth.The annular channel 22 of the mounting cup embraces the bead 27 of thecontainer so that the gasket 26 carried by channel 22 is positioned onbead 27. The lower portion of the skirt 20 is flared outwardly againstthe wall of domed portion 12 adjacent to the head 27. The gasket forms aseal between the skirt and the wall adjacent to the container mouth.

The water-in-oil aerosol spray ofiers a method of dispensing activeproducts that are insoluble in the propellant. Typical propellantsinclude halogenated hydrocarbons, such as chlorofiuoro lower alkanes ofwhich trichloromonofluoromethane, dichlorodifluoromethane anddichlorotetrafluoroethane are illustrative. By dissolving an activeingredient in water and then emulsifying it into the propellant system,a spray product can be formulated. The propellant forms the continuousor oil phase, and the water and active materials constitute thedispersed or water phase. Typical emulsifiers which are useful withchlorofiuoro alkanes include polyglycerides of fatty acids, sorbitanmonolaurate and polyethylene glycol 400 ditriricinoleate.

DETAILED DESCRIPTION OF THE INVENTION The compositions of this inventionwhich form acceptable gaskets for the water-based aerosol products justdescribed, are comprised essentially of a peptized curable elastomericpolymer of 2-chloro-l,3-butadiene dissolved in a volatile organicliquid, and a ternary curing system consisting of about 1 to parts byweight di-o-tolylguanidine, about 2 to 8 parts 2 mercaptoimidazoline andabout 2 to 8 parts dipentamethylenethiuram hexasulfide per 100 parts ofrubber polymer. The improvement achieved by the use of this acceleratorsystem is optimized when there is employed 6 parts, 4 parts and 4 partsof each respective compound per 100 parts of rubber.

As mentioned earlier, the compositions of the invention are composed ofa polymer of 2-chloro-l,3-butadiene dissolved in a volatile organicliquid. This polymer may be either a homopolymer or a copolymer of thebutadiene with minor quantities of other monomers including styrene,acrylonitrile and isoprene. The polymer may be dissolved in a singlevolatile organic liquid or in a mixture of such liquids able to functiontogether as a solvent medium. Preferred usable organic liquids for thispurpose are those that have a minimum boiling point of 230 F. as well asmixtures of liquids that do not boil below 230 F. and yet are capable ofvolatilization from the compositions in the course of the overall dryingand curing cycle to which the gasketing compounds are subjected.Illustrative of this type of liquid are toluene, xylene, a high boilingpetroleum solvent such as Solvesso 100 which has a boiling point rangeof about 230 to 345 R, an aliphatic petroleum solvent such as Varsol #1which boils between 320 and 390 F., and mixtures of such solvents.

The compositions may include a non-volatile liquid plasticizer inquantities ranging between about 0 and 200 parts by weight per 100 partsby weight of polymer. Though their use is not essential, plasticizersfacilitate mixing of the polymer with other ingredients, such asfillers, and also enhance the sealing characteristics of the resultinggasket. When added in quantities of about 200 parts, the plasticizer hasa tendency to exude from the cured composition. Preferably, theplasticizer is used at a level between about 40 and 100 parts by weightto give gaskets having the requisite degree of hardness to insuresatisfactory sealing. Illustrative plasticizers include dioctylsebacate, dioctyl adipate, didecyl phthalate, dioctyl phthalate,naphthenic oils or any relatively non-volatile liquid plasticizingmaterial used as processing aids for neoprene rubber.

While the presence of inorganic fillers is not essential in thesecompositions, their use in sealing aerosol containers tends to reducethe permeability of the gasket to propellants. The fillers are alsohelpful in modifying the specific gravity and how characteristics of thefluid composition. Suitable fillers include hydrated calcium silicate,afine sized whiting, talc, silicon dioxide and clays. The quantity offiller may range between about 0 and 300 parts by weight based on 100parts by weight of polymer. Above about 300 parts, the gasket becomestoo hard and lacks the resilience and elasticity which is desired forsealing purposes. Generally, amounts ranging between about and 200 partsby weight are preferred, though the exact quantity used will depend uponthe selected filler or combination of fillers, the characteristics theyimpart to the fluid composition, and the properties they impart to thecured gasket.

It is also desirable to use a peptizer for the polymer. Peptizers allowgreater ease in adjusting the viscosity of the composition to a valuewithin the range required for standard lining equipment. Typicalpeptizers include alkyl thiuram disulfides, e.g. tetramethyl andtetraethyl thiuram disulfides; piperidinium alkyl dithiocarbamates, e.g.piperidinium pentamethylene dithiocarbamate; and guanidines. Peptizersare used in quantities preferably between about 0.5 and 6 parts byweight based on parts by weight of polymer.

Other ingredients may be incorporated into the composition to impartdesirable properties. These include lubricants, e.g. stearic acid andpetroleum waxes; antioxidants, e.g. diphenyl-p-phenylenediamine and p (ptolylsulfonylamide) diphenylamine; and pigments, e.g. carbon black, ironoxide and titanium dioxide. When lubricants, antioxidants, pigments andother ingredients are employed, they are used in conventional quantitiesto achieve the desired efiect.

The volatile organic liquid is used in quantities such as to givecompositions having a total solids concentration between about 40 and75% by weight, and preferably between about 50 and 65% by weight. Thetotal solids portion of the compositions includes the combined weight ofpolymer, fillers, curing mixture and the other substantiallynon-volatile ingredients employed. With less than about 50% totalsolids, it is difiicult to obtain the thick gaskets required for areosolmounting cups in a single pass through closure lining machinery. Withmore than about 65%, on the other hand, the compositions become quitethick and it is difiicult to maintain the viscosity within a range thatcan be lined on conventional automatic lining machinery.

The invention is further illustrated by the following example whichdescribes a typical composition possessing both a desirable storagestability and the capacity of forming gaskets with satisfactoryresistance to waterbased aerosol products.

EXAMPLE Ingredient: Parts Chloroprene rubber 100 Aluminum silicate clayParaffin wax 2.0 Sodium acetate 1.8 Magnesium oxide 3.0Tetraethylthiuram disulfide 2.5

Ingredient: Parts Piperidinium pentamethylene dithiocarbamate 2.0 Zincoxide 6.25 Diisodecyl phthalate 75 Curing system: I

Di -0 tolylguanidine 6.0 2 mercaptoimidazoline 4.0 Dipentamethylenethiuram hexasulfide 4.0

Toluene added in quantities sufiicient to give a total solids content of62% by weight in the final composition.

The composition was prepared by first milling the poly mer for about oneminute in a Banbury mixer. The sodium acetate, parafiin wax, about 57%by Weight of clay, about 9 parts by weight of diisodecyl phthalate, anda blend composed of the magnesium oxide and about 6 parts by weight oftoluene were then slowly added and to and mixed with the polymer forabout six minutes. The batch was transferred to a Sigma mixer and theremaining amount of clay, the tetraethylthiuram disulfide andpiperidinium pentarnethylene dithiocarbamate were added. The batch wasmasticated for about one hour. About 50 parts by weight of diisodecylphthalate and 200 parts by weight of toluene were then slowly added andmixed for about two hours. A second blend composed of 2mercaptoimidazoline, di-o-tolylguanidine, dipentamethylene thiuramhexasulfide, zinc oxide and the remaining portion of diisodecylphthalate was added and the entire batch was mixed for about 20 minuteswhile maintaining the temperature of the batch below 110 F. Somevolatilization of toluene occurred during processing so that the totalsolids content of the final composition was about 62% by weight. Theviscosity of the freshly-prepared oomposition was about 2000 centipoisesas measured on a Brookfield viscometer, model LVFSX, No. 3 spindle at 30r.p.m. and 85- L2 F.

The storage stability of the composition and the resistance of gasketsobtained from it was measured in the following manner:

The storage stability, or pot life, is determined by the change in theviscosity of the composition which may occur from the time ofmanufacture to the time when the composition is lined in the channel ofan aerosol mounting cup. Since the desired pot life of a satisfactorycompound is a minimum of three months, any compound retaining a lineableviscosity after a three month period is a commercially satisfactorycompound. Limits for lineable viscosities have been set by fieldexperimentation at 1800 to 4200 centipoises. Since no compound of thistype is manufactured with a viscosity greater than 2300 cps., anycompound showing a rise in viscosity of 1900 cps. or less after 3 monthsat room temperature is considered to possess a commercially satisfactorypot life. Moreover, after comparing the viscosity rise of numerouscompounds at room temperature with that at 100 F., it has been concludedthat storage for one week at 100 F. is nearly equivalent to storage forone month at room temperature. The present shelf life testing hastherefore been carried out at 100 F. and a compound showing a viscosityrise of 1900 cps. or less after three Weeks in storage at 100 F. isconsidered commercially stable.

The resistance of gaskets derived from the compositions of the inventionwas tested as follows: A representative portion of the storedcomposition was used to line a number of standard areosol mounting cupsto form sealing gaskets. The cups had an outside skirt diameter closelyapproaching one inch and were thus of the type used to seal metalaerosol containers having a filling opening with an inside diameter of100010.004 inch. The lining was done by depositing the compositionthrough a nozzle into the channel of the cup, the latter being seated ona rotary chuck on standard automatic lining machinery. Lining wascarried out at a rate of 150 to 200 cups per minute. The quantity ofcomposition deposited in each cup averaged about 500 mg. wet weightwhich is equivalent to a dry weight of 310 mg.

The lined cups were dried and cured according to the following schedule:

Time (hr.): Temperature 1 Air dried at ambient temperature. 1 155 F. l200 F. 1 325 F.

The mounting cups containing the cured gasket were tested fordegradation of the gasket in the presence of a water-in-oil emulsion ofthe following composition:

Ingredients: Parts by wt. Naphtha (odorless mineral spirits), RR 244-29l F. 7 Water 53 Toluene 3 Polyglycerol ester of oleic acid (Emcol l4)2 Rating: Description of gasket 1 Not attacked. 2 Mildly attacked. 3Severely attacked. 4 Completely degraded.

The observed ratings were plotted on a graph against the hours ofresidence in the emulsion. The best straight line was then drawn throughthe points plotted. The number of hours needed to achieve a rating of2.5 was then interpolated from the line and was used for comparisionwith similarly tested conventional and experimental compounds.

Upon testing the compound described in the example for shelf life andgasket resistance by the methods just described and on comparison of theresults so obtained with the performance of a conventional gasketingcompound not containing any cure accelerator, it was found that nochange in viscosity occurred in either case after three weeks storage atF. and that the compound of the invention containing the ternaryaccelerator cure system withstood the test emulsion for 1200 hoursbefore undergoing a 2.5 level deterioration. This constitutes a 2.4-foldimprovement over the resistance of gaskets made from conventionalcompounds, a rather remarkable change considering that the additionalcrosslinking process did not, as might well be expected, contribute anunacceptable increase in viscosity of the compound on storage.

It was also determined that this delicate balance of shelf life andgasket characteristics could not be obtained in the absence of any thethree components of the ternary curing system disclosed. In the latterinstances, it was observed that either the cure was insufii-' cient orthe pot life drastically reduced. Also, as mentioned earlier,substantial improvement in gasket resistance could be achieved, withoutcausing the viscosity of the rubber compositions to increase to morethan 1900 cps. after storage at 100 F. for three weeks, by varying theproportions of curing accelerators within about 2 t0 8 parts by weightper 100 parts rubber for the imidazoline and the hexasulfide and about 1to 10 parts for the substituted guanidine.

It is apparent from the foregoing description that it is possible,without departing from the spirit of the invention, to employ the newcritical ternary accelerator curing system to a varied selection ofsolvent-based chloroprene polymer compositions and thereby impart tothem the improved balance of composition and gasket characteristics thatthis ternary system has now been discovered to achieve.

What is claimed is:

1. A gasket-forming composition comprising 100 parts 8 3,397,173 8/1968Collette 260-45.9 3,478,127 11/ 1969 Petersen 260845 3,531,444 9/1970Behrens 26079.5

OTHER REFERENCES by weight of a polymer of 2-chlor0-1,3-butadiene dis- 5solved in a volatile hydrocarbon liquid, and a ternary curing systemconsisting of about 6 parts di-o-tolylguanidine, about 4 partsZ-mercaptoimidazoline and about 4 parts dipentamethylene thiuramhexasulfide.

References Cited UNITED STATES PATENTS 2,006,057 6/1935 Northam 2607843,351,572 11/1967 Jameson 260-5 US. Cl. X.R.

260-237 H, 23.7 M, 41.5 R, 45.9 R, 79.5 B, 779, 793, 797

